S152: COMBINATORY THERAPY OF ASCIMINIB AND PONATINIB WAS EFFECTIVE IN THE TREATMENT OF BLAST PHASE CML CDX MODEL
Authors: Nikola Čuřík, Adam Laznicka, Vaclava Polivkova, Jitka Křížková, Pavel Semerak, Eva Pokorna, Pavla Suchankova, Pavel Burda, Andreas Hochhaus, Kateřina Machová Poláková
Journal: HemaSphere (2023)

Background: CML blast phase (BC-CML) is a heterogeneous disease carrying more lesions than BCR::ABL1. Although patients who progressed to BC-CML during tyrosine kinase inhibitor (TKI) therapy optimally undergo intensive treatment and transplantation their outcome is unsatisfactory. Therefore, there is a need for personalised therapy with novel drugs. Aims: To create CDX model of clonal evolution in BC-CML and to test combinatory therapy with the most potent TKI ponatinib (PON), STAMP-inhibitor asciminib (ASC), and BCL-2 inhibitor venetoclax (VEN). Methods: Five imatinib/ponatinib cross-resistant KCL-22 clones were established and characterized for mutations in BCR::ABL1 and other cancer-related genes. IC50 values for each tested drug were measured. For in vivo experiments equal number of cells of individual clones were mixed and subcutaneously xenotransplanted into NOD-SCID-gamma mice (5x106 cells/mouse; n=42). Mice were randomly divided into 7 groups according to the treatment: 1) control; 2) PON 25 mg/kg b.w.; 3) ASC 30 mg/kg b.w.; 4) VEN 50 mg/kg b.w.; 5) PON+VEN; 6) ASC+VEN; 7) PON+ASC. Treatment was administered perorally once a day after tumor detection (diameter 5 mm in one direction). At the end of the experiment (tumor diameter ≥20 mm in one direction or skin necrosis) mice were euthanised and tumors were homogenised using 70µm cell strainer. Nucleic acids were isolated and NGS mutational analysis of BCR::ABL1 kinase domain and panel sequencing were performed. Results: In the control group of mice, the most proliferated clone during tumor growth was F5 (BCR::ABL1-T315I, -G250E, SETD1B-G1963fs) followed by clones with proliferation fitness in a descendent order E72 (BCR::ABL1-T315I, -Y253H, ZRSR2-R451H) > C7 (BCR::ABL1-T315I, -H396R) > D9 (BCR::ABL1-T315I, -E255V, IKZF1-E383G). Clone D8 (BCR::ABL1-T315I, -I418T, -H396R) did not proliferate. In vitro IC50 values were of predictive value for ASC and PON treatment of the CDX model. Proliferation of clones during ASC therapy in vivo were in descendent order C7>F5>E72>D8>D9, while inversed effect on proliferation was found on PON D9>E72>D8>F5>C7. During combinatory PON+ASC therapy, tumors were unmeasurable during daily drugs administration because of a synergy effect (clones D9 and D8 were sensitive to ASC; clones C7 and F5 were sensitive to PON) and an additive effect of both drugs on the clone E72. Clonal proliferation in vivo during VEN therapy was in the descendent order C7>E72>F5>D8>D9 and tumor growth was significantly delayed compared to monotherapy with ASC and PON, respectively (p>0.001). Combination of PON+VEN also delayed the tumor growth with strong additive effect on the clone D8, which did not grow. Summary/Conclusion: All five established imatinib/ponatinib cross-resistant clones originated from T315I clone of the KCL-22 BC-CML cell line acquired additional mutations in BCR::ABL1 and in 3 clones also in IKZF1, SETD1B, and ZRSR2. Although artificially prepared mixture of cross-resistant clones represented highly resistant model of BC-CML, combinatory therapy with asciminib and ponatinib was potent to suppress tumor growth to immeasurability. The IC50 values of asciminib and ponatinib for each clone were highly predictive and corresponded to in vivo observation of monotherapy. EUTOS 2022, MZCR 00023736 Keywords: CML blast crisis, Animal model, Asciminib, Venetoclax